Control system and method of semiconductor inspection system

ABSTRACT

A control system and method of a semiconductor inspection system are disclosed, wherein the inspection can be conducted without reducing the reliability of measurement even in the case where the supply voltage drops. The control system has a controller, a power supply for a power on-off circuit constituting a switching regulator designed to maintain the output voltage against a supply voltage drop, and a supply voltage drop detector. In the case where a supply voltage drop is detected during the measurement, the measurement is automatically suspended, and after restoring the supply voltage, the measurement is automatically restarted.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a control system of a semiconductorinspection system using a CD-measurement SEM or the like, or inparticular to a control operation against the supply voltage drop.

2. Description of the Related Art

In the semiconductor inspection system using the CD-measurement SEM orthe like, various disturbances including the mechanical vibration andthe external magnetic field are liable to adversely affect thereliability of the inspection result. To cope with this problem,Japanese Patent No. 2911144 (patent Document 1), for example, disclosesa control method for automatically stopping the measurement whenever amechanical vibration or an external magnetic field not smaller than areference value is detected by a detection means.

The reliability of the inspection result is liable to be adverselyaffected also by the supply voltage drop as well as by the externaldisturbances. In the case where the supply voltage drops during themeasurement, therefore, the reliability of the inspection result may beadversely affected. A supply voltage drop, however, poses not only theproblem that the reliability of the inspection result is adverselyaffected but also the problem that the system itself may be shut down.This point is not dealt with by patent Document 1.

To obviate the problem that the system itself may be shut down by thesupply voltage drop, the conventional system uses an instantaneousvoltage drop protector 17 as shown in FIG. 4. The instantaneous voltagedrop protector 17 prevents the supply voltage applied to the system frombeing reduced and the system from being shut down by a supply voltagedrop of a short duration. Also, the reliability of the inspection resultis not adversely affected. The provision of the instantaneous voltagedrop protector 17, however, leads to an increased system cost. Inaddition, the instantaneous voltage drop protector 17 has largefootprints (installation space) and size, resulting in a bulky controlsystem of a semiconductor inspection system.

SUMMARY OF THE INVENTION

In view of the problem described above, the object of this invention isto provide a control system of a semiconductor inspection system, whichis inexpensive and requires no large space as compared with theconventional method using the instantaneous voltage drop protector andin which the inspection can be conducted without adversely affecting thereliability of measurement even in the case where the supply voltagedrops.

According to this invention, there is provided a control system of asemiconductor inspection system, comprising a measurement circuit forelectrically processing the measurement data of an object to beinspected, a controller for controlling the measurement operation of themeasurement circuit, a power on-off circuit for switching on and off thedrive power supplied to the measurement circuit and the controller, a DCpower supply for supplying a DC drive power of a constant voltage to themeasurement circuit, a first switching regulator for supplying the DCdrive power to the controller and a second switching regulator forsupplying the DC drive power to the power on-off circuit.

In the control system of a semiconductor inspection system according tothis invention, the use of the switching regulators makes it possible toconduct the inspection without shutting down the system, at a lower costwith a smaller installation space than in the prior art, even in thecase where the supply voltage drops.

Other objects, features and advantages of the invention will becomeapparent from the following description of the embodiments of theinvention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a control system of a semiconductorinspection system according to an embodiment of the invention.

FIG. 2 shows a supply voltage monitoring circuit according to anembodiment of the invention.

FIG. 3 is a flowchart showing a method of controlling a semiconductorinspection system according to an embodiment of the invention.

FIG. 4 is a block diagram showing the conventional semiconductorinspection system comprising an instantaneous voltage drop protector.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the invention are described below with reference to FIGS.1, 2, 3 below.

First, a control system of a semiconductor inspection system isexplained with reference to the block diagram of FIG. 1. The controlsystem comprises a controller 1 and a measurement circuit 2. Themeasurement circuit 2 is, for example, a measurement unit of aCD-measurement SEM.

The measurement circuit 2, upon receipt of a control signal from thecontroller 1, electrically processes the measurement data of an objectto be inspected. The drive power for the controller 1 is supplied froman exclusive switching regulator 3. This switching regulator 3 suppliesthe controller 1 with the alternating current of a power sourceconverted into a direct current of a constant voltage. The switchingregulator 3 supplies a direct current of a constant voltage to thecontroller 1 even in the case where the AC supply voltage drops. Thisswitching regulator 3 is less expensive and smaller than theinstantaneous voltage drop protector. Consequently, the installationspace required for the control system of a semiconductor inspectionsystem is not substantially increased.

The drive power for the measurement circuit 2 is supplied by a seriesregulator 4. The series regulator 4 supplies the measurement circuit 2with the drive power of the alternating current of the power sourceconverted to a direct current of a constant voltage. The seriesregulator 4 is used as the power source of the measurement circuit 2 toreduce the noises applied to the measurement circuit 2.

Specifically, the measurement circuit of the CD-measurement SEM easilysuccumbs to and develops a measurement failure due to the electricalnoises generated by a chopping system like the switching regulator. Theseries regular generates no electrical noises, and therefore finds asuitable application as a measurement circuit of the CD-measurement SEM.

The measurement circuit other than that of the CD-measurement SEM noteasily affected by the electrical noises requires no series regulator.Nevertheless, the DC power supply for supplying the drive power to themeasurement circuit is required. The DC power supply includes the seriesregulator.

The drive power of the switching regulator 3 and the series regulator 4is supplied from a power source 8 through a power on-off circuit 5 and amolded-case circuit breaker 7. The drive power of the switchingregulator 3 and the series regulator 4 is turned on and off by theon-off operation of the breaker 7.

The power on-off circuit 5 includes an electromechanical contactor 9, anon switch 15 and an off switch 16. The drive power for the power on-offcircuit 5 is supplied by an exclusive switching regulator 6. Theswitching regulator 6 for the power on-off circuit 5 has a similarfunction to the switching regulator 3 for the controller 1, and is lessexpensive and smaller than the instantaneous voltage drop protector. Asa result, a large installation space is not required for the controlsystem of a semiconductor inspection system.

The switching regulators are described in more detail below.

The switching regulators 3, 6 are designed to maintain a constant DCoutput voltage against the drop of the supply voltage.

The switching regulators rectify and smooth the alternating voltage andgenerate a direct voltage by stepping up or down the rectified andsmoothed voltage. The switching regulators can be designed to maintainthe output voltage by increasing the switching pulse width or frequencyeven in the case where the AC supply voltage drops. An example isdescribed in “Transistor Gijutsu SPECIAL No. 28, Comprehensive ModernPower Circuit Technologies”, 1991, by CQ Publishing Co., Ltd., p. 87.Like a wide input voltage range switching regulator described in thisreference adapted to handle the supply voltages of both AC 100 V and AC200 V continuously, the system can be designed to maintain the outputvoltage against the input voltage change as wide as AC 90 V to AC 270 Vby controlling the pulse width and frequency of the switching operation.Also, as disclosed in JP-A-6-237579, the output holding time can belengthened by controlling the switching frequency at the time ofinstantaneous interruption of service.

The switching regulators 3, 6 are each a wide input voltage rangeswitching regulator capable of handling the supply voltages of both AC100 V and AC 200 V continuously in the input voltage range of AC 85 V toAC 264 V. In this way, the output voltage can be maintained even in thecase where the supply voltage drops to 85 V, i.e. 42.5% of the ratedvoltage.

As long as the output of the switching regulators 3, 6 can bemaintained, the inspection can be conducted without shutting down thecontrol system of a semiconductor inspection system.

Next, the supply voltage monitoring circuit is explained.

As described above, as long as the output voltage of the switchingregulator 3 for the controller and the output voltage of the switchingregulator 6 for the power on-off circuit are maintained, the inspectioncan be conducted without shutting down the control system of asemiconductor inspection system. Since the tolerable drop range of thesupply voltage of the series regulator is smaller than that of theswitching regulator, however, a supply voltage, if lower than a criticalvoltage, may cause an unstable supply of the constant-voltage DC drivepower to the measurement circuit 2, and the resulting adverse effect onthe measurement circuit 2 may deteriorate the measurement reliability.The supply voltage monitoring circuit is inserted to cope with thisproblem of deterioration of the measurement reliability.

Specifically, in the case where the supply voltage drops, the outputvoltage of the series regulator 4 drops within a short time. In theseries regulator, the voltage, after being rectified and smoothed thealternating voltage, is stepped down to generate the direct voltage.Once the supply voltage drops below a predetermined voltage (criticalvoltage), the output voltage drops with the supply voltage. Thus, theoutput voltage drops within a short time with the drop of the supplyvoltage.

In the case where the output voltage of the series regulator 4 drops(the supply of the constant-voltage DC drive power becomes unstable),the measurement circuit 2 may be adversely affected to deteriorate themeasurement reliability, even though the control system of asemiconductor inspection system may not be shut down in its entirety.

In the case where the supply voltage of the power source 8 drops,therefore, a supply voltage drop detection signal 19 is transmitted tothe controller 1 by the supply voltage monitoring circuit 18. Thecontroller 1 is so programmed that, upon detection of a supply voltagedrop during the measurement operation, the measurement operation isautomatically suspended, and after the supply voltage is restored, themeasurement is continued automatically. Then, the reliability of thefinal inspection result is secured, in spite of the fact that themeasurement reliability is affected once by a supply voltage drop. Also,since the switching regulators 3, 6 maintain the output voltage even inthe case where the supply voltage drops, the controller 1 operatesnormally and executes the aforementioned process positively. In thisconfiguration, therefore, the reliability of the final inspection resultis not adversely affected even in the case where the supply voltagedrops.

The DC power supply for supplying a constant-voltage DC drive power tothe measurement circuit 2 is not limited to the series regulator. Evenin the case where a DC power supply having a narrow tolerable drop rangeof the supply voltage like the series regulator is used, the provisionof the supply voltage monitoring circuit 18 prevents the reliability ofthe inspection result from being deteriorated even in the case where thesupply voltage drops.

Specifically, once the drop of the supply voltage is detected by thesupply voltage monitoring circuit 18 during the measurement, themeasurement is automatically suspended, and after the restoration of thesupply voltage, the measurement is restarted automatically. Regardlessof whether the output voltage of the power source of the measurementcircuit 2 can be maintained against the drop of the supply voltage,therefore, the reliability of the inspection result is not adverselyaffected.

FIG. 2 shows a configuration of the supply voltage monitoring circuit18.

The supply voltage monitoring circuit 18 includes a transformer 31, arectification and smoothing circuit 39 and a hysteresis comparator 40.

The supply voltage 20 input to the supply voltage monitoring circuit 18is stepped down through the transformer 31, and rectified and smoothedby the rectification and smoothing circuit 39. The output of therectification and smoothing circuit 39 is input to the hysteresiscomparator 40 to determine whether it is not less than a predeterminedvoltage. In the case where the output of the rectification and smoothingcircuit 39 is lower than the predetermined voltage, a supply voltagedrop signal 19 is output. The output of the rectification and smoothingcircuit 39 contains a ripple of twice the frequency of the AC powersource, and therefore the hysteresis comparator 40 is required to have ahysteresis larger than the ripple width. The threshold (corresponding tothe critical voltage) for determining the supply voltage drop in thehysteresis comparator 40 is set to a voltage not lower than the level towhich the output voltage of the series regulator 4 drops. In the casewhere the supply voltage drops and the output voltage of the seriesregulator 4 is likely to drop, the supply voltage monitoring circuit 18outputs the supply voltage drop signal 19.

The flowchart for the method of the control operation based on thesupply voltage monitoring circuit 18 is explained below.

FIG. 3 is a flowchart showing the method of the control operationperformed upon detection of a supply voltage drop according to anembodiment of the invention. After starting the measurement at step 23,the measurement process of step 43 is executed while at the same timedetermining whether the supply voltage is normal or not at step 41. Thedetermination process at step 41 is repeatedly executed until themeasurement process is complete. In the case where the supply voltage isfound to be abnormal at step 41, the process proceeds to step 24 wherethe measurement is suspended. After the measurement is suspended at step24, the process proceeds to step 25 to wait for the restoration of thesupply voltage. In the case where the supply voltage is restored at step25, the process proceeds to step 26 to restart the measurement. Afterthe measurement is restarted at step 26, the measurement process isagain executed at step 43 concurrently with the process of determiningwhether the supply voltage is normal or not at step 41. In the casewhere the supply voltage is detected as abnormal again at step 41, theprocess proceeds again to step 24 to repeat the process shown in theflowchart. Unless the abnormality of the supply voltage is detectedduring the measurement at step 41, the process proceeds to step 27thereby to complete the measurement. According to this control method,the measurement is suspended automatically in the case where the supplyvoltage drops, and the measurement is restarted after the supply voltageis restored. Therefore, the reliability of the inspection result is notadversely affected.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. A control system of a semiconductor inspection system, comprising: ameasurement circuit for electrically processing the measurement data ofan object to be inspected; a controller for controlling the measurementoperation of the measurement circuit; a power on-off circuit for turningon and off the drive power supplied to the measurement circuit and thecontroller; a DC power supply for supplying the DC drive power of aconstant voltage to the measurement circuit; a first switching regulatorfor supplying the DC drive power to the controller; and a secondswitching regulator for supplying the DC drive power to the power on-offcircuit.
 2. A control system of a semiconductor inspection systemaccording to claim 1, comprising a supply voltage monitoring circuit fortransmitting to the controller a signal indicating the drop of thesupply voltage applied to the DC power supply, wherein the controllersuspends the measurement operation of the measurement circuit based onthe voltage drop signal and restarts the measurement operation based ona restoration signal indicating the restoration of the supply voltage toa predetermined value.
 3. A control system of a semiconductor inspectionsystem according to claim 2, wherein the supply voltage monitoringcircuit includes a transformer, a rectification and smoothing circuitand a hysteresis comparator.
 4. A control system of a semiconductorinspection system according to claim 2, wherein a series regulator isused as the DC power supply.